THE NORTH ANATOLIAN FAULT ZONE IN NW TURKEY: INFERENCES FROM NEOGENE STRATIGRAPHY TO EARTHQUAKE RUPTURES

The North Anatolian Fault (NAFZ) is a major tectonic feature of the Marmara region and NW Turkey. It follows an ancient suture zone and comprises three prominent splays. These splays delimit several Neogene basins.

The Neogene basins indicate a sedimentary sequence extending from the Oligocene to Quaternary with noted interruptions in the stratigraphy. The sequence begins with a thick and gently folded limestone that overlies disconformably a pre- Oligocene magmatic/metamorphic basement. It continues with marl-mudstone-tuff intercalations which have an age of the Upper Oligocene-Lower Miocene. The sequence continues with a distinct unconformity and is overlain by lignite bearing marl and fine clastics. It is then cut by volcanics overlain by clastics of both sedimentary and volcanogenic origin. Pleistocene clastics and a thick Holocene alluvium overlie the older units with an angular unconformity.

The sedimentary sequence in NW Turkey indicates a large inland basin modified by tectonic events as evidenced by differing depositional conditions and noted unconformities. The orderly map pattern of Neogene units suggests temporal and spatial modification of Neogene faults possibly dissimilar to the present.

The 1999 earthquakes of the Marmara region caused a surface rupture reaching to a length of over 150km. The rupture included simple as well as complex rupture geometries and slip modes. It extended largely through Quaternary deposits. This rupture pattern is considered to be representing the modern NAFZ with a rather simple through-going geometry. However, details of the rupture appear to bear many influences of the Neogene faults and Neogene fault geometry.